Method for forming a welding spout on a parison during the blowing of a tank

ABSTRACT

The invention relates to a tank of plastics material produced by blow-molding of a parison, incorporating a welding spout, of a shape projecting from its outer surface which has an edge configured to be welded to a corresponding edge of an attached part, the welding spout ending axially, on an inside of the tank, in a shape resulting from contact molding between the parison and a molding component, in which the welding spout ends axially on an outside of the tank in a shape resulting from contact molding between the parison and a molding component.

This application is a Divisional of U.S. application Ser. No.15/108,340, filed on Jun. 27, 2016, which is a National Stage ofapplication PCT/FR2014/053559, filed on Dec. 26, 2014, which claimspriority to FR 1363620, filed on Dec. 27, 2013.

This invention relates to the manufacture of plastics tanks, inparticular fuel tanks.

In order to manufacture tanks from plastics material, multilayerparisons which in particular contain within them a barrier layer, forexample of EVOH, are used. A parison is a foliar or tubular extrudatethat is inserted into a mold and within which excess pressure isestablished to press the said extrudate against the mold to shape itinto the desired shape of the tank.

In order to weld attached parts to tanks of plastics material it isknown that “welding spouts”, that is to say projecting shapes which havean edge, which is generally flat, capable of being heated so as to bewelded to a corresponding edge of an attached part, are known. Theattached part may be a pipe, a connection, a ventilation pipe, the listnot being of any restrictive nature.

The welding spout is formed during blowing of the parison and requiresthat the material constituting the parison should flow substantially insuch a way that the said material will fill a special recess delimitingthe outer shape of the welding spout.

In some cases, as a result of this flow, the barrier layer locatedwithin the parison migrates to some depth in the recess and may belocated close to the area of the welding spout involved in welding. Thiszone is generally defined over a thickness of a few mm, measured fromthe welding plane.

The object of this invention is to provide a new process for forming thewelding spout during blowing of the parison.

In accordance with this process the following stages are carried out ina blowing mold comprising two cavities and an insert, one of thecavities delimiting a recess for forming the welding spout, the saidrecess having a opening opening opposite the insert:

-   -   a push member is provided on the insert opposite the opening of        the recess in the cavity, the push member being capable of        adopting a first position set back from the recess and a second        position in which the push member occupies a portion of the        opening of the recess,    -   the push member is positioned in its first position,    -   the parison is blown so as to match the shape of the cavities,    -   as the parison flows towards the interior of the recess the push        member is advanced into its second position.

As a result of the invention, the presence of the push member in theopening of the recess limits migration of the barrier layer of theparison towards the zone where the welding spout is welded.

In a preferred embodiment provision is also made for a plunger moving onthe cavity to delimit the recess facing the push member, the movingplunger being capable of adopting a first position and a secondposition, the volume of the recess being smaller in the second positionthan in the first, and while the parison is flowing towards the interiorof the recess the moving plunger is placed in its second position.

In practical terms it is simpler for movement of the movable plunger tobe such that the volume of the recess is a maximum when the movingplunger is in its first position and a minimum when the moving plungeris in its second position.

The fact that the moving plunger pushes back the material which hasflowed into the recess further helps to hold the barrier layer at adistance from the welding zone.

In a particular embodiment of the invention, the moving plunger movesconcomitantly with the push member.

Alternatively movement of the moving plunger is initiated after the pushmember has moved.

In a particular embodiment of the invention the push member comprises ahead and a shoulder.

Preferably the push member is dimensioned in such a way as to allow playbetween the head of the push member and the parison in the secondposition and in a direction transverse to movement of the push member.Such play is obtained for example in accordance with the followingformula, where A is the distance measured between the head of the pushmember and the cavity measured in the direction of movement of the pushmember, B is the distance measured between the head of the push memberand the cavity measured in the direction transverse to the movement ofthe push member, and C is the distance between the shoulder of the pushmember and the cavity in the direction of movement of the push member:A=4/B and C≥6 mm

Through its construction distance C corresponds to the thickness of theparison at the shoulder of the push member.

In accordance with the invention plastics materials are understood to bematerials comprising at least one synthetic resin polymer.

All types of plastics materials may be suitable. Suitable plasticsmaterials will belong to the category of thermoplastic materials.

By thermoplastic material is intended any thermoplastic polymer,including thermoplastic elastomers, as well as mixtures thereof. By theterm “polymer” is intended both homopolymers and copolymers (inparticular binary or ternary ones). Examples of such copolymers are,without limitation: randomly distributed copolymers, sequencedcopolymers, block copolymers and graft copolymers.

All types of thermoplastic polymers or copolymers whose melting point isbelow the decomposition temperature are suitable. Syntheticthermoplastic materials which have a melting point range extending overat least 10 degrees Celsius are particularly suitable. An example ofsuch materials are those which have polydispersity of their molecularmass.

In particular polyolefins, thermoplastic polyesters, polyketones,polyamides and their copolymers may be used. A mixture of polymers orcopolymers may also be used, as well as a mixture of polymeric materialswith inorganic, organic and/or natural fillers such as, for example, butnot limited to: carbon, salts and other inorganic derivatives, naturalor polymer fibres. It is also possible to use multilayer structurescomprising stacked incorporated layers comprising at least one of thepolymers or copolymers described above.

A polymer often employed is polyethylene. Excellent results have beenobtained with high density polyethylene (HDPE). Preferably tanks alsoincorporate a layer of resin which is impermeable to fuel such as forexample EVOH (partly hydrolysed ethylene-vinyl-acetate copolymer).Alternatively or in addition it may undergo surface treatment(fluorination or sulfonation) in order to render it impermeable to fuel.

The invention also relates to a tank of plastics material derived frommolding by blowing a parison incorporating a welding spout, that is tosay a shape projecting from its outer surface which has an edge capableof being welded to a corresponding edge of an attached part, the saidwelding spout ending axially on the inside of the tank in a shaperesulting from molding by contact between the parison and a moldingelement.

As claimed in particular advantageous but optional characteristics ofthe invention, which may be adopted alone or in combination:

-   -   the welding spout ends axially on the inside of the tank as an        internal rim in the form of a ring,    -   the welding spout ends axially on the outside of the tank as a        shape resulting from contact molding between the parison and a        molding element,    -   the welding spout ends axially on the outside of the tank as a        radial flat surface in the form of a ring,    -   the welding spout comprises an internal rim in the form of a        ring set back from the radial planar surface,    -   the welding spout has a shape not derived by revolution so as to        offer better mechanical strength.

The invention will be better understood from a reading of the appendedfigures, which are provided by way of example and are not in any waylimiting, in which:

FIG. 1 is a view in elevation of a fuel tank provided with a fillingpipe.

FIG. 2 is a view in cross-section of a part II of the tank in FIG. 1,showing a welding spout in a first embodiment.

FIG. 3 is a perspective view of the same part II, seen from above.

FIG. 4 is a perspective and cross-sectional view along the plane III-IIIin FIG. 3,

FIG. 5 is a view similar to that in FIG. 4, along a plane IV-IVperpendicular to plane III-IIII.

FIG. 6 is a view similar to that in FIG. 2 of another embodiment of theinvention.

FIG. 7 is a view similar to that in FIG. 6, in a perpendicularcross-sectional plane.

Reference is now made to FIG. 1, in which a tank 1 of generic shape maybe seen. In reality the shape of the tank will depend on the vehicle,but this shape is of no importance in the context of the invention,which applies to tanks of all shapes. This tank will have beenmanufactured by the blowing of a parison, as is known, within a blowingmold (not illustrated). An example of such manufacture is described forexample in EP 1110697 A2, the contents of which are incorporated in thisdescription as a reference.

The tank is a multilayer tank, of high density polyethylene (HDPE) withat least one layer of EVOH (partly hydrolyzed ethylene-vinyl acetatecopolymer), which ensures a seal against hydrocarbons and is referred toas a “barrier layer”.

Tank 1 comprises a filling pipe 3 which is intended to connect the fuelcap (not shown) of the vehicle to tank 1. Pipe 3 is connected to tank 1by welding. For this purpose it comprises a material compatible with thematerial of which the tank is made, at least in the regions which are incontact with these two welded components.

For welding with pipe 3 the tank has a welding spout 5, which can beseen in FIGS. 3 to 5.

Welding spout 5 projects from the outer surface 7 of the tank, here inthe form of a protrusion that is generally flared derived by revolution,which terminates axially in a radial planar surface 9 in the shape of aring.

Flat surface 9 is a welding surface, to which the end of filling pipe 3is welded after the parison has been shaped by blowing in order tosecure said filling pipe 3 to tank 1 in a strong leaktight manner.

In FIG. 4 it will be seen that in addition to flat surface 9 weldingspout 5 has an internal rim 11 on the outside of the tank which, likeflat surface 9, faces the outside of tank 1. Internal rim 11 forms aring of smaller diameters which lies set back from flat surface 9. It isflat and parallel to said surface 9. Because of the presence of internalrim 11, internal surface 13 of spout 5 ends in a shape which isgenerally flared, with a stepped cross-section. Flat surface 9 andinternal rim 11 may have any shape, provided that they allow the weldingspout to be used to connect the tank to an external accessory such aspipe 3, but in accordance with the invention these shapes result fromcontact molding between sheet 18 (or more generally the parison) and amolding element, as will be seen subsequently.

On the inside of the tank the welding spout ends axially in a secondinternal rim 14, similar to first internal rim 11, that is to sayforming a ring of smaller diameters set back from internal surface 8 ofthe tank. Internal rim 14 may have any shape, but in accordance with theinvention it is the result of contact molding between sheet 18 (or moregenerally the parison) and a molding element, as will be seensubsequently.

As will be seen in FIG. 5, the outer lateral surface 15 of welding spout5 is cylindrical, except for two diametrically opposite grooves 17 whichcan be seen in FIGS. 3 and 4.

These grooves 17 are used for positioning a finishing tool in order toperform finishing operations on the tank after it has been molded, andin particular the drilling of spout 5, as will be describedsubsequently.

Furthermore these grooves 17 prevent the welding spout from having ashape derived by revolution, that is to say one which does not changethroughout any rotation about its axis, which provides better mechanicalstrength for the welding spout according to tests performed by theinventors.

The process as claimed in the invention will now be described through aparticular and non-limiting embodiment.

As described in EP 1110697 A2, a parison comprising two sheets 18 ofmultilayer plastics material is extruded from an extrusion die and islowered into a mold (not shown).

This mold comprises two matching halves, known as shells or molds orcavities, and a central insert which may be placed between two shells.

In accordance with the known process, once the two sheets of the parisonhave been lowered between the cavities on either side of the insert,each of the two cavities closes on the insert in such a way as to closethe mold for a first time. Excess pressure of gas, generally air, isthen established between the insert and each sheet of the parison insuch a way as to press the sheet against the internal wall of the cavityand impart shape to it. This stage is described as blowing. As blowingtakes place, accessories previously installed on the insert and carriedby suitably moving structures are advanced in the direction of one orother of the sheets, applied against the sheet and welded to it. Thisoperation makes it possible to insert various accessories such asventilation valves and pipes into the tank without having to insert theminto the mold after molding. After this shaping the two cavities eachbearing a sheet of the parison move away from the insert and the latteris withdrawn from between the two cavities. The two cavities are finallycaused to approach each other in such a way as to close the mold for asecond time, this time bringing the peripheries of the two sheets intocontact, peripheries which weld to each other and form the tank.

The invention to which this application relates is implemented in thecourse of performance of this known process during its blowing stage.

It may be required to form a welding spout on one or both of sheets 18of the parison, depending upon the desired functions for the tank. Herethe invention only describes a single welding spout and a single sheet18, but this indication is not in any way limiting.

FIG. 2 illustrates two moving inserts 19 and 21 which will be describedas moving plunger 19 and push member 21 on either side of the sheet 18of the extruded parison. Push member 21 is carried by the insert (notshown, it is located below sheet 18 in relation to FIG. 2), while movingplunger 19 is carried by one of the two cavities (not shown, the cavitybearing moving plunger 19 is located above sheet 18 in relation to FIG.2). Around moving plunger 19 the shell also comprises a spout mold 23,in two parts, 23A and 23B, which are capable of moving within the planeof the figure between a closed position which may be seen in FIG. 2 andan open position in which each of two parts 23A and 23B is separatedfrom the other by a sufficient distance to allow the spout to bereleased from the mold after it has been shaped in spout mold 23.

Spout mold 23, in combination with moving plunger 19, delimits a recess31 for forming a welding spout. This recess 31 has an opening 25 whichopens out opposite the insert.

Push member 21 comprises a head 21A and a shoulder 21B. It faces opening25 of recess 31. It is capable of adopting a first position set backfrom recess 31, which can be seen in FIG. 2, and a second position shownas a dashed line in FIG. 2 in which it occupies part of the opening 25of recess 31. The movement of push member 21 from the aforesaid firstposition to the aforesaid second position is shown by arrow 27.

Moving plunger 19 may also move as indicated by arrow 29 between aset-back position as shown in FIG. 2 and a forward position illustratedby a dashed line.

Thus moving plunger 19 is capable of adopting a first position in whichthe volume of recess 31 is a maximum and a second position in which thevolume of recess 31 is a minimum.

In the second position, referred to as the forward position, movingplunger 19 bears against the plastics material of the parison and bymolding imparts to it its final shape delimited by the dashed line onthe side of the cavity of the mold.

In the first position, referred to as the set-back position, movingplunger 19 allows the material of the parison to move forward in recess31 if it experiences a thrust from the direction of the insert in themold, in particular through the effect of the excess pressure during thestage of blowing the parison.

In order to implement the invention the following stages are carried outduring the blowing stage in a process for shaping a tank.

In this stage the parison of two sheets 18 is extruded and each shape 18is placed between the insert and each of the two cavities of the mold.The mold is closed onto the insert.

Moving plunger 19 and push member 21 are placed in their firstpositions. Spout mold 23 is closed, in the position in FIG. 2.

Subsequently air is injected under pressure between each sheet 18 andthe insert to shape it to the shape of the cavity against which it isthus pushed. This blowing causes the plastics material of sheet 18 toflow towards and into recess 31. Sheet 18 then forms a hollow 18A on theside of the insert.

While the material of sheet 18 is flowing towards the interior of recess31 push member 21 is advanced into its second position, shown by adashed line. The head 21A of the push member penetrates recess 31 andshoulder 21B bears against sheet 18. Sheet 18 then adopts a shapecorresponding to the side of the insert, as indicated by the dashedline. In particular push member 21 plays the part of a molding componentwith regard to the sheet and forms a flat portion 30 corresponding tofuture internal rim 14.

In a second operation, determined in relation to the operatingconditions during blowing, which are defined in particular by thethickness of the parison, the duration and pressure of blowing, and thetemperatures of the components present, moving plunger 19 is placed inits second position shown by a dashed line.

Sheet 18 thus adopts the corresponding shape, with flat radial surface 9in the shape of a ring and an internal flat surface 12 corresponding tofuture internal rim 11 previously described with reference to FIG. 4. Inother words moving plunger 19 acts as a molding component with regard tosheet 18.

Once push member 21 and moving plunger 19 have both reached their secondposition, they remain immobile until the end of the blowing stage.Depending upon the different parameters for molding the tank, theinvention may take place throughout the entire blowing stage (in whichcase it begins at the same time as air is injected under pressure andends when the blowing pressure ceases) or only part of the blowing stage(for example it may start after air has been injected and/or end beforethe blowing pressure ceases).

After sheet 18 has been sufficiently cooled to allow the tank to bereleased from the mold, the two cavities of the mold separate, spoutmold 23 opens and the tank is released from the mold.

In a finishing operation the wall of the tank is then drilled out to itsentire thickness between flat portion 12 and flat portion 30 so as tocut out the internal surface 13 of the spout and define internal rims 11and 14. A drilling tool which is fastened onto grooves 17 of spout 5 isused for this purpose.

In the embodiment illustrated in FIGS. 6 and 7 a push member 21′ whosehead 21′A is smaller than that 21A of push member 21 previouslydescribed is used. Push member 21′ thus leaves lateral play betweensheet 18 and head 21′A which makes it possible to control flow of thematerial in a better way when forming the welding spout.

Having regard to distance A measured in the direction of movement of thepush member between head 21′A of the push member and the cavity,distance B measured in a direction transverse to the movement of thepush member between head 21′A of the push member and the cavity anddistance C measured in the direction of movement of the push memberbetween the shoulder of push member 21′B and the cavity, it will befound that ratio A/B is less than 4 and that the value of C is less than6 mm.

Measurements made by the inventors on tanks manufactured as claimed inthe invention have shown that the barrier layer of the multilayerparison lies at a sufficient distance from surface 9 so that subsequentwelding of this surface 9 to an attached part such as a pipe does notdamage this barrier layer. This adequate positioning of the barrierlayer within the wall of the tank is the result of the action of movingplunger 19, accentuated by that of push member 21, in the course of theblowing stage.

Furthermore, with a multilayer parison comprising virgin material andground up material (such as for example is obtained from the recovery ofrejects), the distribution of the layers of the multilayer parisonremains fairly uniform, whereas without the action of plunger 19 it hasbeen found that virgin material tends to be lacking in the welding spoutwhile ground up material tends to be present there in excess quantity.

The invention is not limited to the embodiments presented and otherembodiments will be clearly apparent to those skilled in the art.

The invention claimed is:
 1. A tank of plastics material produced byblow-molding of a multilayer parison comprising at least a barrierlayer, incorporating a welding spout, of a shape projecting from theouter surface of the tank, the welding spout having an external radialshape resulting from contact molding between the parison and a spoutmold, the welding spout ending axially, on an inside of the tank, in ashape resulting from contact molding between the parison and a firstmolding component, and in which the welding spout ends axially on anoutside of the tank in a shape resulting from contact molding betweenthe parison and a second molding component, the shape having an edgeconfigured to be welded to a corresponding edge of an external attachedpart, the second molding component being different from the firstmolding component, both being configured to contact the multilayerparison during blow-molding allowing the edge to be welded of thewelding spout to be distant from the barrier layer of the multilayerparison.
 2. The tank as claimed in claim 1, wherein the welding spoutends axially on the inside of the tank in an internal rim in a shape ofa ring.
 3. The tank as claimed in claim 1, wherein the welding spoutends axially on the outside of the tank in a radial flat surface in ashape of a ring.
 4. The tank as claimed in claim 3, wherein the weldingspout comprises an internal rim in a shape of a ring set back from theflat radial surface.
 5. The tank as claimed in claim 1, wherein thewelding spout has a shape.